40 BULLETIN 826, TJ. S. DEPARTMENT OF AGRICULTURE. 
mediates between apterous and alate viviparous forms are of quite 
common occurrence and indicate possible origin of the apterous 
forms. It is no doubt true, however, that in members of this tribe 
the equilibrium is disturbed more easily than in some of the others, 
and that external influences have a more sudden and noticeable 
effect. 
We have divided the tribe into four subtribes which may be 
separated as follows: 
Key to the Subtribes op the Aphtdini. 
1. Body covered with long projections : Cervaphidina. 
Body naked with the exception of a few hairs 2. 
2. Head without prominent antennal tubercles Aphidina. 
Head with prominent antennal tubercles 3. 
3. Wings with the radial sector normal Macrosiphina. 
Wings with the radial sector more or less united with the upper branch of 
the media or hind wings reduced Pentalonina. 
Subtribe APHIDINA. 
The insects in the Aphidina show a great variation in regard to 
the cornicles and cauda. Some have very markedly developed 
cornicles, others have extremely small ones, while one genus lacks 
them altogether. The cauda varies from very large in genera like 
Hyalopterus to scarcely any visible cauda in some of the other 
genera. Certain of the genera appear more similar than others, for 
example, Hyalopterus, Pergandeidia, and Brachycolus all have small 
cornicles and somewhat large caudse. Certain other genera, while 
appearing quite different in some ways, are evidently related. 
Cavariella, Hyadaphis, Aspidaphis, and Vesiculaphis all have char- 
acters which are very suggestive, although there are differences 
between them. So also there is a group suggesting Aphis. The 
various genera may be separated as follows: 
Key to the Genera of the Aphidina. 
1. Cornicles absent Asiphonaphis. 
Cornicles present. „ 2. 
2. Cornicles swollen, not sub cylindrical or tapering 3. 
Cornicles eubcylindrical or tapering but sometimes extremely short and 
ringlike .• 12. 
3. Fore wings with the media once branched; apterous form with very much 
swollen cornicles Vesiculaphis. 
Fore wings with the media twice branched 4. 
4. Hind wings with the cubitus lacking Carolmaia. 
Hind wings with both media and cubitus present 5. 
5. Abdomen with a dorsal projection or tubercle above cauda 6. 
Abdomen without this structure 7. 
